(1) Field of the Invention
The invention relates to a method and a system for localizing an attenuation change location in an optical waveguide within an optical transmission system.
(2) Description of the Related Art
In an optical transmission system, data are transmitted by light pulses via an optical waveguide between a transmitter and a receiver. The length of such an optical waveguide can be a number of kilometers. The optical waveguide is formed for example by a fibre-optic cable. The optical waveguide is composed of mineral glass, for example silica glass, or of organic glass or plastic. An optical waveguide is a dielectric waveguide. An optical waveguide is used primarily as transmission medium for line-conducted telecommunications methods. However, optical waveguides are also used for the transmission of energy, for example for the transmission of UV light for illumination purposes, and in metrology for example in infrared thermometers and spectrometers.
Fibre-optic cables are used in communications technology primarily for transmitting information over wide distances with a high bandwidth. In the case of optical fibres a distinction is made between graded-index fibres and stepped-index fibres. The refractive index decreases towards the outside in the radial direction continuously in the case of graded-index fibres, and in stepwise fashion in the case of a stepped-index fibre. The so-called multimode optical fibres can be formed as graded-index fibres and as stepped-index fibres. In contrast thereto, single-mode optical fibres are formed primarily by stepped-index fibres. In the case of a multimode optical fibre, different individual light waves (modes) are used for signal transmission. On account of a plurality of possible light paths, instances of signal influencing occur on account of propagation time differences, such that multimode optical fibres are less suitable than single-mode optical fibres for transmitting messages over large distances at a high bandwidth. Single-mode optical fibres can bridge distances of hundreds of kilometers without repeaters, i.e. without intermediate amplification.
One disadvantage of conventional optical transmission systems is that in the event of a disturbance of the optical waveguide, for example as a result of a fracture of the optical fibre on account of construction work, the location of the disturbance cannot be localized in order to rectify the disturbance.
A further disadvantage of conventional optical transmission systems consists in the risk that the transmitted light signals can be coupled out by bending of the optical waveguide, such that the transmitted information can be intercepted by third parties without the receiver being able to ascertain this.